In communications of image data and voice data in the packet network, where a small delay is allowable, when the congestion occurs in a communication network between the terminals, a delay in transmission of the packet increases and a packet loss occurs. Therefore, a smooth regeneration becomes difficult or impossible.
For solving the delay in transmission and the packet loss, there is a method for notifying a sending terminal of the delay in transmission, packet loss rate, etc. obtained by measuring a receiving state at a receiving terminal and changing a sending bit rate and an encoding rate to avoid the congestion.
As disclosed in U.S. Pat. No. 2,616,657, there is also a method for coping with the congestion at an early stage by setting a relay node between the terminals. Further, concerning on an increase of the delay in transmission, there is a method for accepting a certain delay by setting a buffer in a side of the receiving terminal.
Concerning on detection of the congestion state in the network, as disclosed in Published Patent Application Hei 07-303117, there is a method for judging by comparing the packet loss rate or a throughput or a roundtrip time with one or two or more threshold values.
In controlling the congestion when the congestion is detected, there is a method for avoiding or easing the congestion by controlling the sending bit rate and the encoding rate step by step.
There is also a method for reserving a communication bandwidth in the network from the terminal before communication and maintaining a necessary communication bandwidth for preventing the occurrence of the congestion. However, according to this method, when it is impossible to maintain the communication bandwidth, a connection is rejected.
When a packet is lost, for utilizing data in the packet, there is a method of requesting retransmission of the lost packet or generating the lost packet from a redundant packet and the packet received at the receiving terminal by sending the redundant packet.
In coping after detecting the congestion, even if the congestion is detected early, the sending bit rate and the encoding rate are changed later. Therefore, the congestion state continues for a while until being coped with.
For detecting the congestion, there are methods for detecting by the terminal and in the relay node. For detecting in the relay node and the receiving terminal, it is necessary to inform at least the sending terminal after detecting the congestion. Therefore, an additional packet is sent during the congestion, and there is a possibility that the congestion becomes worse.
This invention was intended to solve the above-stated problems. This invention aims at predicting the congestion from an earlier state of the network for preventing the congestion.
For judging the state of the network and detection of the congestion by a parameter, e.g., packet loss rate or throughput, roundtrip time, etc., there is a possibility that the judgement is affected by data due to a temporary noise.
For solving the above-stated problems, this invention aims at reducing the influence from the temporary noise by judging in combining a plurality of parameters and achieving more accurate judgement. This invention also aims at realizing an effect by using a method for deriving a value used in judgement with less influence from the noise.
When the sending bit rate and the encoding rate are controlled step by step after judging the state of the network and detecting the congestion, an amount of a change due to a difference, rate, etc. used in judging and detecting tends not to reflect on the control. Therefore, there is a problem that a sufficient effect is not realized in a result of the control on the state of the network and the congestion. Further, when the state is recovered from the congestion state, there is a problem that a sufficient effect is not realized also in a quick recovery from the dropped sending bit rate and encoding rate.
This invention is intended to solve this problem and improve the accuracy in the control.
For assigning a communication bandwidth, communication protocol for assigning queuing in communication between the terminal and the relay node in the network must be packaged. It is necessary that the communication protocol is packaged in the terminal and the relay node between the terminals. There is a problem that even if the communication protocol is packaged only between the terminals, it is not sufficient. This is disclosed in U.S. Pat. No. 2,616,657 for example.
This invention intends to solve this problem and simplify a configuration of the communication system.
For correcting an error of the lost packet, there is a problem that if the error is corrected by resending, it is too late for regeneration time, and the congestion becomes worse as the resending request increases at the time of the congestion. There is also a problem that when a redundant packet is sent, a communication bandwidth which can be used for sending an original packet becomes narrower.
This invention intends to solve this problem and correct the error without worsening the congestion while sending the original packet efficiently.
As stated, it is a primary aim of this invention to predict the congestion by sending a report on the receiving state at the receiving terminal to the sending terminal, preventing the congestion in advance based on the prediction, and securing real-time quality of the communication.